Precisely spherical bodies, and especially those which are hollow and with thin walls, are utilized as targets in inertial confinement fusion reactors, and have other applications as well. One technique for forming precisely spherical bodies is to heat a preformed hollow sphere or a piece of material containing a bubble forming (expansion) agent, to a temperature at which it is molten, and to drop the body so that it moves in free fall to allow surface tension to form it into a sphere. If the body falls through static air, it is subject to deformation by the air resistance. Although a body can be dropped through a vacuum drop tower, difficulties can be experienced by the fact that the body will remain in a vacuum drop tower of reasonable height, for only a short period of time, so it is desirable to form the body as close to a perfect sphere as possible before it is dropped and begins cooling. Also, it is desirable to avoid sudden gusts of gas in the drop tower, that would be encountered if the vacuum drop tower were suddenly opened to gas at atmospheric pressure in order to admit the molten body. A method and apparatus for forming rounded objects such as spheres, with high precision, and in a relatively simple manner, would be of considerable value.
High temperature melts are very difficult to process without contamination, because they tend to corrode the crucibles that contain them. High-purity melts are important in the fabrication of semiconductor devices and many other applications. A method and apparatus that could contain a melt during processing, without contamination, would be of considerable value.